The presence of lymphocytotoxic antibodies was studied in 22 patients receiving granulocyte transfusions. Due to previous blood transfusions 7 out of 22 patients had lymphocytotoxic antibodies before granulocyte transfusions were started. 6 out of 15 unsensitized patients developed antibodies during granulocyte transfusion therapy, and 9 out of 15 patients had no detectable antibodies at any time. Transfusion reactions occurred in the presence of lymphocytotoxic antibodies not directed against donor cells.